Steel wire for steel cord used as a reinforcing member in a radial tire of an automobile or various kinds of belts and hose, or steel wire for sawing wire generally uses, as a material, a wire rod with a wire diameter, i.e., diameter, of 4 to 6 mm that has undergone adjusted cooling after hot rolling. This wire rod undergoes primary wire drawing to be steel wire with a diameter of 3 to 4 mm. Then, the steel wire is subjected to intermediate patenting treatment and further undergoes secondary wire drawing to have a diameter of 1 to 2 mm. After that, the steel wire is subjected to final patenting treatment and then to brass plating. Then, the steel wire undergoes final wet wire drawing to be steel wire with a diameter of 0.15 to 0.40 mm. High-carbon steel wire obtained in this manner is further subjected to twisting in a manner that a plurality of high-carbon steel wires are twisted together to form a twisted steel wire; thus, steel cord is produced.
In recent years, for a reduction in production cost of steel wire, intermediate patenting mentioned above is omitted and wire drawing is performed directly from a wire rod that has undergone adjusted cooling into 1 to 2 mm, which is a wire diameter after final patenting treatment, in more and more cases. This requires the wire rod that has undergone adjusted cooling to have direct wire drawing characteristics from a wire rod, i.e., so-called rod drawability, and high ductility and high workability of a wire rod are required increasingly strongly.
For example, as described in Patent Literatures 1 to 7, many suggestions have been made for a technique of improving wire drawability of a wire rod that has undergone patenting treatment. For example, Patent Literature 1 discloses a high-carbon wire rod in which a pearlite structure has an area fraction of 95% or more, and the average nodule diameter and the average lamellar spacing in the pearlite structure are 30 μm or less and 100 nm or more, respectively. Moreover, Patent Literature 4 discloses a high-strength wire rod containing B. These conventional technologies, however, cannot reduce wire-breaks that accompany an increase in wire drawing speed and an increase in wire drawing working ratio, or provide an effect of improving wire drawability enough to influence working cost in wire drawing.